Experimental And Kinetic Modeling Study On Ignition Delay Of Binary Fuel Blends Of Methyl Hexanoate With N-butanol And Ethanol

With the energy crisis intensifying and people’s awareness ofenvironmental protection enhancing, a new engine combustion technologycalled HCCI (Homogenous Charge Compression Ignition) and thebiodiesel have attracted the attention of researchers. Biodiesel is amultiple-component mixture of monoalkyl esters of long-chain fatty acidscontaining12~18carbon atoms. A good knowledge of the kineticsmechanism of the reaction of biodiesel fuels is necessary to performreliable simulations of ignition, combustion, and emissions inhomogeneous charge compression ignition (HCCI) and diesel engines.Methyl hexanoate as a fatty acid methyl ester with7carbon atoms caneffectively show the ignition characteristics of biodiesel and can be studiedat current RCM by introducing the intake air heating. To learn about theignition delay features of methyl hexanoate, methyl hexanoate/n-butanoland methyl hexanoate/ethanol mixture, the effects of temperature, pressureand mixing ratio in rapid compression machine (RCM) were studied.Kinetics model was built to predict the ignition delay and simulate thecombustion process. The main reaction pathways involved in the binaryfuel oxidation were delineated. Over the conditions researched in this study,conclusions can be summarized as follows:(1) Ignition delay of methyl hexanoate, methyl hexanoate/n-butanoland methyl hexanoate/ethanol mixture showed obvious three regimes ofoxidation, namely cool flame, negative temperature coefficient, and hightemperature oxidation. Ignition delay of binary fuel decreases withcompression pressure increasing，and increases with the proportion of n-butanol or ethanol increasing. Knocking degree of binary fuelcombustion weakens by increasing the n-butanol proportion. Ignition delayof binary fuel also increases with dilution ratio increasing.(2) Kinetics model gave fairly well prediction on the ignition delay ofmethyl hexanoate, methyl hexanoate/n-butanol and methylhexanoate/ethanol mixture at different experimental conditions.(3) Methyl hexanoate, n-butanol and ethanol shows two-stage heatrelease during low temperature and single-stage heat release during hightemperature.(4) N-butanol has an obvious effect on the of reaction pathways ofmethyl hexanoate in high temperature and slight effect in low temperatureoxidation. Carbon chain length of alcohol molecules has great influence onits ignition delay. Ethanol has longer ignition delay than n-butanol.